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L. Hoffart, G. Georges, L. Siozade, O. Casadessus, J. Conrath, C. Deumié; Scattering Properties of Edematous Human Corneas. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5815.
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The transparency is the main characteristic of the corneal tissue, necessary to allow transmission of the entire visible incident light. This property is ensured by the highly ordered stratified structure of the stroma, coupled to small variations in the refractive index. The other layers: epithelium, the bowman’s and Descemet’s membrane and endothelium, act also to maintain this property. When the endothelial cell density falls below a critical density (200 to 400 cells/cm²), following trauma, inflammation or dystrophy, the endothelium fails to regulate the corneal hydration and edema gradually develops.The tissue becomes opaque and may mildly or strongly deteriorate the vision. This loss of transparency depends not only to the transmission coefficient but also to the losses by scattering and absorption.Currently, ophthalmologists characterize this loss of transparency empirically by characterizing the effect observed visually or by measuring the thickness of the edematous cornea.
When illuminating sample, heterogeneities (surface or bulk) interacts with the incident light and re-emit in all directions in space. The amplitude and phase of the incident wave are then modified and are characteristic of microstructures that create it. The analysis of the scattered light intensity, in terms of intensity or phase, provides information on the microstructure of the cornea. Both scattered intensity and polarization of scattered light are then measured. Angle Resolved Scattering (ARS) and Ellipsometry of Angle Resolved Scattering(EARS) techniques are used.
The aim of this paper is to characterize the scattering optical properties of cornea grafts more or less edematous, and to link ARS measurements to the empirical clinical observations. To complete these results, EARS measurements are performed and allow to determine the origin (surface or bulk) of the scattered signal by studying the polarimetric behavior of corneal grafts edema.
The results of these measurements, focused on a backscattering space, reveal a link between light scattering from graft human cornea and the pathology degree. Surface effects dominated scattering signal. But OCT measurements shows the bulk contribution that should be quantify.
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